In cellular systems, further improvement in communication speeds is required, and a radio communication system in conformity to an LTE (Long Term Evolution) standard whose maximum transmission speed exceeds 100 Mbps is being put in practical use. LTE intends to improve multipass tolerance, for example, by using OFDMA (Orthogonal Frequency Division Multiple Access) for downlink access and by using SC-FDMA (Single Carrier-Frequency Division Multiple Access) for uplink access, and to improve a spectrum efficiency by introducing MIMO (Multiple-Input Multiple-Output) transmission that uses multiple antennas in a transceiver and a receiver.
The cellular system covers a wide range of area, as a whole of the cellular system, by arranging a high number of base stations each covering a communication area of, for example, about a few hundred meters in a service area. The communication area that the base station covers is called a cell. However, there is a case where there exists an environment to which an electric wave from an outdoor base station called a macro base station is hard to reach, mainly in indoor environments such as high story floors in a building and in the underground. As a technology of securing the communication area in indoor environments like this, the distributed antenna system (DAS: Distributed antenna system) is known.
As conventional technologies, the distributed antenna systems are described in Japanese Unexamined Patent Application (Translation of PCT Application) No. H11 (1999)-501172 and Japanese Unexamined Patent Application Publication No. 2010-268192. Moreover, 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2,” TS36.300, V10.2.0, 2010/12, pp. 119-120 discloses a technology of reducing interferences from other base stations in LTE-Advanced that is a development standard of the LTE.